Durand's apothecary shop in Philadelphia seems to have been something of a center for botany and botanists in America. He went out of his way to make it physically spectacular, importing marble countertops, mahogany cabinets, and the like from France (where he got the money for this, I don't know). He also collected many botanical books and journals, and made these available to botanists. He funded some botanical explorers and bought their plant collections, acquiring the herbaria of Nuttall and Rafinesque. He himself undertook the two major expeditions listed above, and of course collected extensively in the Phiadelphia area.
The herbarium references are from Humphrey, who notes for instance that Durand went to Paris in 1868

"and took with him his herbarium of more than 10,000 species and 100,000 specimens. This he presented to the Musée du Jardin des Plantes, where it was placed in a special room as the Herbier Durand." p. 77